erm, isnt this the reason for large squads and rotation? upto managers to look after their players.
that said, the actual point of why have a pointless competition squeezed in at the end of the season seems valid. on other hand would they be saying the same if it were warm up friendlies for the WC this June?
Agree with your first point.
As for the second point, the Nations League is a halfway house between major tournaments and meaningless friendlies. It gives managers a chance to try out players without really losing too much kudos if you lose. People used to moan about a friendly where the whole team get's changed at half time. Damned if you do damned if you don't.